Dual sensor camera

ABSTRACT

A dual sensor camera that uses two aligned sensors each having a separate lens of different focal length but the same f-number. The wider FOV image from one sensor is combined with the narrower FOV image from the other sensor to form a combined image. Up-sampling of the wide FOV image and down-sampling of the narrow FOV image is performed. The longer focal length lens may have certain aberrations introduced so that Extended Depth of Field (EDoF) processing can be used to give the narrow FOV image approximately the same depth of field as the wide FOV image so that a noticeable difference in depth of field is not see in the combined image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/570,736 (now U.S. Pat. No. 9,118,826), entitled “DUAL SENSOR CAMERA,”filed on Dec. 15, 2014 by at least one common inventor, which is acontinuation of then U.S. patent application Ser. No. 14/035,635 (nowU.S. Pat. No. 8,913,145), entitled “DUAL SENSOR CAMERA,” filed on Sep.24, 2013 by at least one common inventor, which is a continuation ofthen U.S. patent application Ser. No. 12/727,973 (now U.S. Pat. No.8,542,287), entitled “DUAL SENSOR CAMERA,” filed on Mar. 19, 2010 by atleast one common inventor, which claims the benefit of U.S. ProvisionalApplication No. 61/161,621, entitled “DUAL SENSOR CAMERA,” filed on Mar.19, 2009, all of which are incorporated herein by reference in theirentireties.

BACKGROUND

Digital camera modules are currently being incorporated into a varietyof host devices. Such host devices include cellular telephones, personaldata assistants (PDAs), computers, and so forth. Consumer demand fordigital camera modules in host devices continues to grow.

Host device manufacturers prefer digital camera modules to be small, sothat they can be incorporated into the host device without increasingthe overall size of the host device. Further, there is an increasingdemand for cameras in host devices to have higher-performancecharacteristics. One such characteristic that many higher-performancecameras (e.g., standalone digital still cameras) have is the ability tovary the focal length of the camera to increase and decrease themagnification of the image, typically accomplished with a zoom lens, nowknown as optical zooming. Optically zooming is typically accomplished bymechanically moving lens elements relative to each other, and thus suchzoom lenses are typically more expensive, larger, and less reliable thanfixed focal length lenses. An alternative approach for approximatingthis zoom effect is achieved with what is known as digital zooming. Withdigital zooming, instead of varying the focal length of the lens, aprocessor in the camera crops the image and interpolates between thepixels of the captured image to create a “magnified but lower-resolutionimage. There have been some attempts to use two different lenses toapproximate the effect of a zoom lens. It has been done in the past withfilm cameras in which the user could select one of two different focallengths to capture an image on film. More recently, a variation on thisconcept with camera modules has been disclosed in U.S. Pat. Pub. No.2008/0030592, the entire contents of which are incorporated herein byreference, which discusses a camera module with a pair of sensors, eachhaving a separate lens through which light is directed to the respectivesensor. In this publication, the two sensors are operated simultaneouslyto capture an image. The respective lenses have different focal lengths,so even though each lens/sensor combination is aligned to look in thesame direction, each will capture an image of the same subject but withtwo different fields of view. The images are then stitched together toform a composite image, with the central portion of the composite imagebeing formed by the relatively higher-resolution image taken by thelens/sensor combination with the longer focal length and the peripheralportion of the composite image being formed by a peripheral portion ofthe relatively lower-resolution image taken by the lens/sensorcombination with the shorter focal length. The user selects a desiredamount of zoom and the composite image is used to interpolate valuestherefrom to provide an image with the desired amount of zoom.Unfortunately, the disclosure in this publication is largely conceptualand lacks in certain details that would be needed to provide optimalperformance.

The foregoing examples of the related art and limitations relatedtherewith are intended to be illustrative and not exclusive. Otherlimitations of the related art will become apparent to those of skill inthe art upon a reading of the specification and a study of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a camera.

FIG. 2 is an illustration of the combination of two images into a singlecombined image.

FIG. 3 is an illustration of digital zooming of the combined image.

DETAILED DESCRIPTION

The following description is not intended to limit the invention to theform disclosed herein. Consequently, variations and modificationscommensurate with the following teachings, and skill and knowledge ofthe relevant art, are within the scope of the present invention. Theembodiments described herein are further intended to explain modes knownof practicing the invention and to enable others skilled in the art toutilize the invention in such, or other embodiments and with variousmodifications required by the particular application(s) or use(s) of thepresent invention.

A camera 10 is shown in FIG. 1. The camera 10 may include a first lens12 having a relatively-shorter focal length and a first sensor 14 thatare located proximate to and substantially aligned with a second lens 16having a relatively-longer focal length and a second sensor 18. Byhaving the combined first lens and first sensor aligned with thecombined second lens and second sensor, the sensors can each obtain animage of substantially the same subject. Of course, due to the differentfocal lengths of the lenses 12 and 16, the first sensor 14 will obtainan image of the subject with a relatively-wider field of view (FOV) ascompared to the relatively-narrower FOV of the image obtained by thesecond sensor 18.

In most cases, each sensor 14 and 18 would perform certain basic imageprocessing algorithms such as white balancing, and so forth. The secondlens 16 has an additional reference

number 17 to indicate that it is designed to work with Extended Depth ofField (EDoF) processing, which may involve introducing specificmonochrome or chromatic aberrations into the lens design as determinedby the EDoF technology, or by adding a phase mask (e.g., a cubic phasemask) to the lens. Each sensor may also perform additional imageprocessing such as EDoF processing. In this example, the EDoF processing20 is shown as part of sensor 18 and is not a part of sensor 14. Inother examples, not illustrated here, each of the sensors 14 and 18 mayinclude EDoF processing, or other combinations may be employed such assensor 14 including EDoF processing while sensor 18 does not. Similarly,while this example shows only the second lens 16 being designed to workwith EDoF processing, any other combination may be possible, includingeach of the lenses 12 and 16 being designed to work with EDoFprocessing. The lenses 12 and 16 could be made of any acceptablematerial, including plastic, glass, optical ceramic, diffractiveelements, or a composite.

EDoF processing will be discussed here generally, but much greaterdetail can be found in the literature associated with the followingcompanies that are believed to be actively developing EDoF technology:DxO Labs, S.A. of Boulogne, France (under its DIGITAL AUTO FOCUS™trademark); CDM Optics, Inc. of Boulder, Colo. (under its WAVEFRONTCODING™ trademark); Tessera, Inc. of San Jose, Calif. (under its OPTIMLFOCUS™ trademark); and Dblur Technologies Ltd. of Herzliya Pituach,Israel (whose relevant IP assets are now owned by Tessera)(under itsSOFTWARE LENS™ trademark). In addition, the following patents, publishedpatent applications, and technical articles are believed to discloserelated EDoF technology: PCT/FR2006/050 197; PCT/FR2008/05 1265;PCT/FR2008/05 1280; U.S. Pat. No. 5,748,371; U.S. Pat. No. 6,069,738;U.S. Pat. No. 7,031,054; U.S. Pat. No. 7,218,448; U.S. Pat. No.7,436,595; PCT/IL2004/00040; PCT/IL2006/01294; PCT/IL2007/00381;PCT/IL2007/000382; PCT/IL2007/00383; PCT/IL2003/000211; and Dowski &Cathey “Extended Depth of Field Through Wavefront Coding,” AppliedOptics, 34, 11, p. 1859-66 (1995); the contents of each of which areincorporated herein in their entirety.

Depth of field refers to the depth of the longitudinal region in theobject space that forms an image with satisfactory sharpness at somefocus position. In ordinary optics, the paraxial depth of field isdetermined by the allowable paraxial blur, the lens focal length, andthe lens f-number. See for example, Warren J. Smith, Modern OpticalEngineering, 3rd Edition, Chapter 6. Within the paraxial model, thedepth of field of the lens is fixed once these choices are made.

A more sophisticated model of depth of field in ordinary optics includesthe lens aberrations and diffraction effects. This model typicallyanalyzes the depth of field using through focus Modulation TransferFunction (MTF) calculations. In this model, the depth of focus dependson the aberrations of the lens and the diffraction occurring at thef-number of the lens. The depth of field is determined by these factorsplus the focal length of the lens. As the aberrations become smaller,the depth of field of the lens approaches a limit set by diffraction,which is determined by the lens f-number, the focal length of the lens,and the allowable MTF drop at various object distances. Similarly to theparaxial depth of field model, the maximum depth of field is set by theallowable blur (MTF drop), the lens f-number, and the lens focal length.

In the ordinary optical design process, the goal is to minimize theaberrations present in the lens, consistent with size and costconstraints. The goal is form a sharp image when the lens is in focus.In extended depth of field (EDoF) technology, the depth of field isincreased by a combination of the use of a specially designed lenstogether with EDoF image processing of the image captured by the sensor.Various types of EDoF technology have been proposed or implemented byvarious companies (some of which are mentioned above).

The various EDoF technologies all require that the lens not form thesharpest image possible at best focus, but rather form an image that isdegraded in a special way. In one implementation, this is achieved witha phase mask, which “degrades” the image. In other implementations, thisis achieved by introducing specified monochromatic or chromaticaberrations into the lens design. A sharp image is then recoveredthrough signal processing techniques. The details of how the image isdegraded and how it is recovered differ between the various EDoFtechnologies.

In the design of a lens for use with EDoF technology, the goal is not tominimize the aberrations present in the image formed by the lens, butrather to introduce with the use of a phase mask or a special set ofaberrations into the image formed by the lens that allows recovery of asharp image over an extended depth of field. The exact aberrations ortype of phase mask that must be introduced depends on the particularEDoF technology in use. In some cases, these aberrations are introducedby the addition of an additional optical element, such as a cubic phaseelement (or cubic phase mask), to an otherwise sharp lens. In othercases, axial color or monochromatic aberrations may be introduced intothe lens design itself.

In the example shown in FIG. 1, lens 16 has certain aberrations thereinthat are designed for use with the EDoF processing 20 that will beperformed by the sensor 18 that corresponds to the lens 16. In thisexample, the lens 16 may be a lens having a focal length of 7.2 mm, afieldof-view (FOV) of 32 degrees, and an f-number of f/2.8. The lens 12may be a lens having a focal length of 3.62 mm, an FOV of 63 degrees,and an f-number of f/2.8. These lens specifications are merely exemplaryand any other suitable lens characteristics could be acceptable. Inaddition, one or both of the lenses 12 and 16 could be variable focallength (zoom) lenses.

In the example shown in FIG. 1, the two lenses 12 and 16 have the samef-number so that the illuminance of the light received at the sensors 14and 18 is equivalent. With equivalent illuminance, the sensors can beoperated at similar levels of amplification and with similar exposuretimes. In this manner, the separate images captured by the separatesensors 14 and 18 can be of similar levels of brightness and contrast.By having similar levels of amplification, the background noise in eachimage will be similar. By having similar exposure times, artifacts ineach image due to subject motion will be similar. By maintainingsimilarity as to these two characteristics in the two images, thecomposite image formed from the two images will be more acceptable tothe user.

Examples of sensors that could be used for sensor 18 are Model Nos.VD6826 and 69031953 (each of which include DxO EDoF algorithms) andVD68031853 (which includes Dblur EDoF algorithms), each of which areavailable from STMicroelectronics of Geneva, Switzerland. Examples ofsensors that could be used for sensor 14 are these same sensorsmentioned above (with EDoF processing turned off) or similar sensorsthat do not have EDoF capabilities, such as VD6852 or VD6892. In thisexample, each of the sensors is a Bayer sensor, which uses a colorfilter array over the array of separate pixels, as is well known. Suchsensors sense green light at every other pixel, with the interveningpixels alternating between red pixels and blue pixels. The raw sensedsignals are later provided to a demosaicing algorithm, whichinterpolates between the pixels to obtain a full color signal for eachpixel. However, the invention is not limited to use with a Bayer sensorand will work equally well with sensors having a different color filterarray, cameras based on time-sequential color, cameras usingbeamsplitters and separate sensors for each color channel, and othercamera architectures, provided these architectures are consistent withthe operation of one of the underlying EDoF technologies.

In some cases, the camera 10 may be considered to include only thefunctional portions described above. In other cases, these portions(referred to collectively as a camera module 22) may also be combinedwith certain downstream components as part of the camera 10. In suchcase, the camera 10 may also include an image signal processor (ISP) 24,a display 26, and user interface controls 28. Of course, as is wellknown in the camera industry, cameras may also typically include severalother components that are omitted here for simplification. For example,as non-limiting examples, these other components may include batteries,power supplies, an interface for the application of external power, aUSB or other interface to a computer and/or printer, a light source forflash photography, auto-focus and image stability controls, internalmemory, one or more ports for receiving an external memory card ordevice (e.g., an SD or xD memory card), and in the case of the use of acamera in a mobile phone, a microphone, speaker, transmitter/receiver,and an interface for an external microphone and speaker (e.g., aBluetooth headset).

The user interface controls 28 may include conventional controls thatare used to operate the camera, including controls to instruct thecamera to capture one or more images, as well as to manipulate theimages, and many other functions. The display 26 may be a conventionaldisplay that displays images automatically as directed by the ISP 24 orupon request by the user via the user interface controls 28 and ISP 24.The ISP 24 includes certain distortion-correction algorithms thatsmoothly match features between the two separate images when thecomposite image is formed. Further, the ISP 24 may include thedemosaicing algorithm (referenced above with regard to Bayer sensors),sharpening algorithms, and other standard algorithms used in ISPs insuch applications. The ISP also includes algorithms to create thecombined image from the two captured images. A suitable approach forcombining the images is discussed in U.S. Pat. Pub. No. 2008/0030592,referenced above.

FIG. 2 shows both the image 50 from the first sensor (the one with thewider FOV) and the image 52 from the second sensor (the one with thenarrower FOV). The wide FOV image 50 goes through up-sampling 54, whilethe narrow FOV image 52 goes through down-sampling 56. In order toensure that the two images are combined to form a single congruent imagewithout any visible mismatch between the appearance of image objects,the wider FOV image 50 commonly undergoes an image up-sampling operation(i.e. digital zoom) whose scaling factor, A, may range from 1 (i.e. noup-sampling operation applied) to Z, where Z is the ratio of FOV of thefirst sensor to the ratio of FOV of the second sensor. The narrow FOVimage 52 undergoes a down-sampling operation whose scaling factor, B, isgiven by Z divided by A. Hence, the relationship between the two scalingfactors is generally given by the equation:Z=A×B

The amount of up-sampling 54 and down-sampling 56 represents a differenttrade-off between the sharpness quality and the size of the combinedimage. The up-sampling factor is generally controlled by the “digitalzoom” setting selected by the user; however, it is possible to select avalue of A which does not match the “digital zoom” setting in orderconstrain the number of pixels in the combined image. After the wide FOVimage 50 has been up-sampled it may optionally go through furthersharpening 58. Then the wide FOV image 50 has a mask 60 applied thereto,which serves to block a central portion 62 of the image 50 whileallowing a peripheral portion 64 of the image 50 to be used in formingthe combined image 66. After the narrow FOV image 52 has beendown-sampled it has a mask 68 applied thereto, which serves to block aperipheral portion 70 of the image 52 while allowing a central portion72 of the image 52 to be used in forming the combined image 66. Asdifferentiated by a border 74 in the combined image 66, the centralportion 76 of the combined image 66 is taken from the narrow FOV image52 while the peripheral portion 78 of the combined image 66 is takenfrom the wide FOV image 50.

FIG. 3 shows the digital cropping of the peripheral region of thecombined image 66 such that the resulting image has a smaller FOV 80corresponding to the “digital zoom” setting specified by the user. Thismay be referred to as “digital zooming” of the combined image 66. Inthis figure, the central portion 76 of the combined image 66 isdifferentiated from the peripheral portion 78 by the border 74 (althoughthe border 74 will not actually be visible to a user in operation). Inone zoomed image 82, the camera 10 has been zoomed to a position whereonly the central portion 76 of the combined image 66 (which is thenarrow FOV image 52) is used. At the other end of the spectrum, anotherzoomed image 83 can be created, in which the combined image 66 is used.At an intermediate position in the spectrum, a different zoomed image 84can be created. For this image, the central portion 76 of the combinedimage 66 is expanded and only a fraction of the peripheral portion 78 ofthe combined image 66 is used.

Alternatively, the camera module 22 could include one or more ISPslocated thereon. They could be separate from or integrated into thesensors. Further, while the lenses 12 and 16 described herein are fixedfocal length, either or both could be variable focal length (zoom)lenses.

It should be appreciated that with the camera 20 described above, thecombined image will have similar levels of brightness, background noise,motion artifacts, and depth-of field. This will make for a more pleasingand acceptable combined image. If the EDoF technology were not utilized,this would be impossible to achieve. This is because with conventionaloptics it is not possible to get the same illuminance delivered to theimage plane from two lenses of different focal length while at the sametime matching the depth of field. One can choose to have the same imageilluminance; for example, by each of the lenses having an f-number off/2.8. But in such case, the depth of field will be much greater for theshorter focal length lens. Alternatively, one can choose to have thesame depth of field; for example, with the focal lengths for the twolenses used in the example described above in conjunction with FIG. 1,the longer focal length lens would need to have an f-number ofapproximately f/11 to have the same depth of field of the shorter focallength lens. But in such case, the optical power delivered by the longerfocal length lens (at f/11) would be 1/16^(th) of the optical powerdelivered by the shorter focal length. The camera 10 described aboveallows for the optical power and depth of field to be the same for eachlens/sensor combination. Of course, it would also be possible to obtainthe same optical power and depth of field with different focal lengthlenses if the two different image sensors were operated with differentamounts of amplification or with different exposure times.Unfortunately, this would change the background noise level or motionartifact level, respectively, between the two images.

One variation on the disclosure above is that there could be some typeor pre-cropping of the peripheral and central regions of the wide FOVimage prior to the-upsampling operation (to reduce the processing andmemory requirements of the image processing involved in the upsamplingoperation).

Any other combination of all the techniques discussed herein is alsopossible. The foregoing description has been presented for purposes ofillustration and description. Furthermore, the description is notintended to limit the invention to the form disclosed herein. While anumber of exemplary aspects and embodiments have been discussed above,those of skill in the art will recognize certain variations,modifications, permutations, additions, and subcombinations thereof. Itis therefore intended that the following appended claims and claimshereafter introduced are interpreted to include all such variations,modifications, permutations, additions, and sub-combinations as arewithin their true spirit and scope.

We claim:
 1. A method of generating a combined image with a camera, themethod comprising: receiving light with a first sensor from a first lenshaving a first focal length; capturing a first image formed on the firstsensor with the first sensor; receiving light with a second sensor froma second lens having a second focal length that is longer than the firstfocal length; capturing a second image formed on the second sensor withthe second sensor, the combination of the first sensor and the firstlens and the combination of the second sensor and the second lens beingdirected toward the same subject; and combining the first image and thesecond image together to form a single combined image with the secondimage forming a central portion of the single combined image and aperipheral portion of the first image forming a peripheral portion ofthe single combined image; and wherein the step of combining the firstand the second images includes at least one of up-sampling the firstimage and down-sampling the second image; and when the first image isup-sampled, the first image is sharpened after the up-sampling.
 2. Themethod of claim 1, wherein the up-sampling is performed with a scalingfactor A and the down-sampling is performed with a scaling factor B. 3.The method of claim 2, wherein: Z is the ratio of the field of view(FOV) of the first sensor to the FOV of the second sensor; andZ=A×B.
 4. The method of claim 3, wherein A is a value in the rangebetween and including 1 and Z.
 5. The method of claim 2, wherein: A is avalue in the range between and including 1 and Z; and Z is the ratio ofthe field of view (FOV) of the first sensor to the FOV of the secondsensor.
 6. The method of claim 1, further comprising applying a mask tothe first image before the first image is combined with the secondimage, the mask blocking a central portion of the first image andallowing the peripheral portion of the first image to be used in formingthe single combined image.
 7. The method of claim 1, further comprisingapplying a mask to the second image before the second image is combinedwith the first image, the mask blocking a peripheral portion of thesecond image and allowing a central portion of the second image to beused in forming the single combined image.
 8. The method of claim 1,wherein the first lens and the second lens have substantially equalf-numbers.
 9. The method of claim 1, wherein the first lens and thesecond lens are selected such that the illuminance on the first sensorand the illuminance on the second sensor are equivalent.
 10. The methodof claim 1, wherein the amount of up-sampling is determined based atleast in part on a digital zoom setting selected by a user.
 11. Themethod of claim 1, wherein the central portion and the peripheralportion of the single combined image have similar levels of at least oneof brightness, background noise, motion artifacts, and depth of field.12. The method of claim 1, wherein: the second lens has been designed towork with extended depth of field (EDoF) processing by the introductionof specified aberrations into the second image formed on the secondsensor; and the second image is subjected to EDoF processing to focusthe second image.
 13. The method of claim 12, wherein: the first imagehas a first depth of field determined by the combination of the firstsensor and the first lens; and the EDoF processing of the second imageresults in the second image having a second depth of field that issubstantially equal to the first depth of field.
 14. The method of claim12, wherein: the first lens has been designed to work with extendeddepth of field (EDoF) processing by the introduction of specifiedaberrations into the first image formed on the first sensor; and thefirst image is subjected to EDoF processing to focus the first image.15. A method of generating a combined image with a camera, the methodcomprising: receiving light with a first sensor from a first lens havinga first focal length; capturing a first image formed on the first sensorwith the first sensor; receiving light with a second sensor from asecond lens having a second focal length that is longer than the firstfocal length; capturing a second image formed on the second sensor withthe second sensor, the combination of the first sensor and the firstlens and the combination of the second sensor and the second lens beingdirected toward the same subject; and combining the first image and thesecond image together to form a single combined image with the secondimage forming a central portion of the single combined image and aperipheral portion of the first image forming a peripheral portion ofthe single combined image; and wherein the step of combining the firstand the second images includes at least one of up-sampling the firstimage with a scaling factor A and down-sampling the second image with ascaling factor B; Z is the ratio of the field of view (FOV) of the firstsensor to the FOV of the second sensor; andZ=A×B.
 16. The method of claim 15, wherein A is a value in the rangebetween and including 1 and Z.
 17. The method of claim 15, wherein thefirst lens and the second lens have substantially equal f-numbers. 18.The method of claim 15, wherein the first lens and the second lens areselected such that the illuminance on the first sensor and theilluminance on the second sensor are equivalent.
 19. The method of claim15, wherein the amount of up-sampling is determined based at least inpart on a digital zoom setting selected by a user.
 20. The method ofclaim 15, wherein the central portion and the peripheral portion of thesingle combined image have similar levels of at least one of brightness,background noise, motion artifacts, and depth of field.
 21. The methodof claim 15, wherein: the second lens has been designed to work withextended depth of field (EDoF) processing by the introduction ofspecified aberrations into the second image formed on the second sensor;and the second image is subjected to EDoF processing to focus the secondimage.
 22. The method of claim 21, wherein: the first image has a firstdepth of field determined by the combination of the first sensor and thefirst lens; and the EDoF processing of the second image results in thesecond image having a second depth of field that is substantially equalto the first depth of field.
 23. The method of claim 21, wherein: thefirst lens has been designed to work with extended depth of field (EDoF)processing by the introduction of specified aberrations into the firstimage formed on the first sensor; and the first image is subjected toEDoF processing to focus the first image.